The present invention relates to a method for manufacturing a dimensionally-stable shaped article for use as ceiling coffers.
Ceiling tiles presently in use are generally made of pressed paper pulp or porous glass fiber and may be covered with various coatings to improve fire-resistance and for decorative purposes. Polystyrene foam or polyurethane foam is also used to produce what are commonly known as "luminous ceilings". Panels for such luminous ceilings are commonly sold in standard sizes of 3 feet .times. 3 feet. These luminous ceiling panels may be formed in a wide variety of configurations, e.g. dish-shaped or bowl-shaped, and of considerable depth, providing intersecting visual effects in combination with lighting fixtures.
Dimensionally-stable shaped shrink-proof articles may be moulded to produce almost any contour imaginable, replacing concrete, asbestos cement, moulded plastics, conventional wall paneling, plaster and the like. The articles are lightweight, strong, resistant to fire and acid, and do not give off toxic gases and are economical to produce because neither considerable pressure nor heat is required in the manufacture.
For example, in U.S. Pat. No. 1,962,577, which issued on June 12, 1934, in the name of David Wolochow, a method of producing molded compositions from asbestos is disclosed wherein chrysotile asbestos fibres, in the form of short fibres, sand or dust, is mixed with a mineral acid, for example, phosphoric acid; the mixture is applied to a mold and subsequently dried at a temperature exceeding 100.degree. C.
It is indicated that if the drying is effected at room temperature, the molded product will have some strength after a considerable length of time, but the shrinkage is too great to give a satisfactory product. Thus, the disclosed process requires drying at elevated temperatures. Moreover, the use of asbestos fibres for molding large complex shapes is not practicable or economical. That is, the application of high pressure would be required to ensure adequate shape retention. The use of fibres also makes it very difficult to maintain a uniform wall thickness in the molded article.